The present invention is directed to the molding of plastic containers or articles and, more particularly, to a molding system and related method using combined blow molding and injection molding techniques to form an article or container having a smooth outer surface adjacent to a closed end thereof.
The use of molded plastic containers continues to grow in the consumer market at a rapid rate and promises to continue in years to come. For many products, such as liquid or semi-liquid (viscous) cosmetics or the like, the plastic container, such as a bottle or jar, is by far the most popular. Advantageously, a plastic container is not only non-breakable, but can be molded into different shapes so as to be very attractive, as well as functional. In addition, from a cost standpoint, the use of plastic is competitive with the other materials often used to form containers, such as glass.
One of the most popular containers used for cosmetics, as well as other liquid and semi-liquid products, is the blow molded bottle or jar. Usually, the containers are fabricated of a clear, translucent or opaque plastic material. For example, polyethylene terephthalate (PET) with additives for varying light transmission and/or color is used to form most types of cosmetic containers. Of course, other materials can also be chosen depending on various factors, such as the type of product contained, the desired size or shape of the container, the expected or required service life, any recycling/environmental considerations, or inherent cost constraints.
In addition to merely containing the product, the container should have an appearance that is pleasing to the eye, since the aesthetics may ultimately influence the customer""s decision to select one product over another and/or consummate the purchase. As noted above, the attractiveness of the container may be significantly enhanced by forming it having a distinctive or irregular shape, as well as by using eye-catching colors and intricate surface patterns or designs. Many different types of containers embodying some or all of these features are well known in the art, and are commonly used as part of an overall marketing strategy in an effort to boost sales over the competition.
In the case of the popular blow molded plastic container, a preform created using conventional injection molding techniques is blown and/or stretched into a mold cavity, usually with the simultaneous application of heat. The preform is typically formed in a tubular shape, with a neck adjacent to the open end and a xe2x80x9cbottomxe2x80x9d area at the opposite, closed end that may form the support surface or bottom of the resulting container once blow molding is complete. The neck normally includes the opening that receives the blow air and/or stretch rod, as well as the threads that allow for a cap or cover to be removably secured to contain and/or dispense the product held in the container. The neck typically does not experience any stretching during blow molding, which allows the size and shape of the threads and opening to be predetermined.
One limitation resulting from the conventional injection molding process is the creation of a mark or vestige in the preform at the location where the material is injected through a gate in the mold leading to the cavity. In the usual process, this gate mark is located at the outside surface adjacent to the closed end of the tubular preform. Hence, it is also present at this same location in the resulting blow molded article or container.
For articles or containers that are positioned upright in use, the gate mark is usually hidden from view and does not significantly detract from the overall aesthetics or appearance (although from a functional standpoint, it may be necessary to contour the bottom portion of the blow mold cavity such that a support lip or ledge is defined around the gate mark to prevent it from affecting the ability of the article or container to stand upright). However, the presence of the gate mark on the container is still unacceptable in some instances, including when: (1) the container is inverted in use, in which case the outer surface adjacent to the closed end of the preform becomes the outer surface of the upper portion of the container; and/or (2) a decoration, such as a stamping, engraving, label, or the like is to be placed on the closed end of the container over the area where the gate mark is usually located.
To move the gate mark to a less obtrusive location, others in the past have proposed using a side or neck gating technique to form an injection molded preform that is later blow molded into a hollow container. Perhaps the earliest examples are found in U.S. Pat. Nos. 3,947,176 and 3,881,854, both to Rainville, which concern forming spherical, smooth bottomed, blow-molded articles, such as Christmas ornaments, using combined injection and blow molding techniques. A more recent example is found in Coca-Cola""s U.S. Pat. No. 5,965,081 to Schloss et al. The ""081 patent is primarily directed to forming a multi-layered preform using side gating techniques, which is supposed to enhance the strength of the bottom area of the resulting blow molded container by eliminating the undesirable crystallization that results from the conventional location of the gate mark at the closed end. The disclosures of each of these patents are incorporated herein by reference.
While these techniques may allow for the creation of a blow molded container having the desired smooth outer surface along a closed end, it is extraordinarily difficult in practice to ensure that the injection material penetrates or reaches all areas of the corresponding mold cavity when only a single side or neck gate is used. If sufficient penetration is not achieved, air bubbles, thin areas or holes may be created in the preform, which may render it unsuitable for later use in blow molding. While defective containers created from such misformed preforms may of course be recycled, the end result is an increase in cost and a decrease in the efficiency of the overall molding operation. Accordingly, the need for an improvement in the combined injection and blow molding art, especially in terms of reliability and efficiency, is identified.
In accordance with a first aspect of the invention, a method of forming a container having an open end and a closed end using combined injection and blow molding techniques is disclosed. The method includes injecting a material through a side gate into an injection mold cavity having a closed end portion, drawing the material into the injection mold cavity using a vacuum, and cooling the material in the mold cavity to form a tubular preform with a closed end having a substantially smooth outer surface. The method further includes blow molding the preform to create the container having a predetermined shape. As a result of forming the preform using the side gate along with a vacuum assist, the resulting blow molded container has a substantially smooth outer surface along the closed end that is free from defects.
In one embodiment, the injection mold cavity includes a neck portion, and the injecting step comprises injecting the material through the gate to the neck portion of the injection mold cavity. Also, at least a portion of the injection mold cavity may be defined by a porous material, in which case the step of drawing the material into the injection mold cavity comprises placing a vacuum source in fluid communication with the porous material. The vacuum action thus created assists in ensuring that the injection material completely fills the injection mold cavity. Preferably, at least part of a closed end portion of the injection mold cavity is defined by the porous material. Also, the step of drawing the material into the injection mold cavity may comprise substantially completely evacuating the mold cavity prior to injecting the material. The method may also include the step of heating one or both of an injection core or pin and at least one portion of the injection mold bounding the injection mold cavity, possibly including the porous material or insert, prior to the injecting step.
The step of blow molding the preform to create the container may comprise positioning the preform in a mold having at least two mating mold portions. The blow mold thus defines a cavity contoured to provide the container with a cross-sectional shape selected from the group consisting of substantially square, rectangular, circular, elliptical, or triangular. In one particular embodiment, the step of blow molding the preform to create the container includes positioning the preform in a mold having at least two mating portions that define a pyramid-shaped blow mold cavity. Accordingly, the resulting container is pyramid-shaped and includes a substantially smooth support surface. The step of blow molding may further include stretch blow molding a preform in a blow mold cavity using a stretch rod such that a portion of the preform is forced into engagement with a corresponding portion of the blow mold.
In addition, the method may further comprise the step of either embossing, engraving, or printing an indicia or placing a label on a smooth support surface of the container. This step may include placing a label or decal in a blow mold adjacent to the closed end of the preform prior to blow molding, or simply applying the label or decal on the container once it is removed from the mold.
In accordance with a second aspect of the invention, a system for molding an aesthetically and functionally enhanced container is disclosed. The system comprises an injection mold including a closed-end mold cavity for receiving an injection material through a side gate for forming a tubular preform having an open end and a closed end with a substantially smooth outer surface. A vacuum source is provided in communication with the mold cavity for drawing the material into the mold cavity to form the preform. The preform is then expanded using a blow mold apparatus to form the container, which as a result of the side gating and vacuum assist has a substantially smooth outer surface that is free from defects or gate marks.
In one embodiment, the injection mold cavity includes a neck portion for forming a neck of the preform adjacent to the open end thereof. The side gate may be located at or adjacent to the neck portion of the injection mold cavity, and may further include a conical exit portion so as to minimize the point of contact made with the preform once injection is complete. Also, at least a portion of the injection mold is comprised of a porous material at least partially defining the closed end of the injection mold cavity, in which case the vacuum source communicates with the porous material to maintain the vacuum in the injection mold cavity. To further improve the flow of material into the injection mold cavity, a heater may also be provided for heating one or more portions of the injection mold, including one or both of the core or pin and the porous material, prior to injecting the material.
In accordance with a third aspect of the invention, a method of forming an aesthetically and functionally enhanced container using combined injection and blow molding techniques is disclosed. The method comprises maintaining a vacuum in an injection mold cavity having a neck portion and a closed end portion for creating a tubular preform having an open end; injecting a material into the injection mold cavity through a gate located adjacent to the neck portion of the injection mold cavity and substantially away from the closed end portion; and cooling the material in the injection cavity to form the preform and create any mark or vestige of the gate at the neck portion adjacent to the open end. The preform then undergoes blow molding to create the container with an opening and a closed end having a substantially smooth outer surface.
In accordance with a fourth aspect of the invention, a system for molding an aesthetically and functionally enhanced container from a preform is disclosed. The system comprises an injection mold including a mold cavity having a closed end and a neck portion communicating with a side gate. Material is injected into the cavity through the side gate to form a tubular preform with an open end and a closed end having a substantially smooth outer surface. A vacuum source is provided for creating a negative pressure in the injection mold cavity at least partially during the injection of the material, and preferably both before and during the injection process. A blow molding apparatus is also provided for forming the preform into a container having a preselected shape. The resulting container is substantially free of defects and includes a closed end having a substantially smooth outer surface as the result of the positioning of the gate in the injection mold and the vacuum assist.
In accordance with a fifth aspect of the invention, a product container formed by blow molding a preform created by an injection molding process is disclosed. The container comprises a body having an opening for receiving a product, at least three sidewalls, and a connector wall contiguous with the sidewall. The connector wall and sidewall each have a substantially smooth outer surface with no gate mark or vestige resulting from the injection molding of the preform from which the container is formed. In one embodiment, the three sidewalls and the contiguous connector wall are each triangular in shape, whereby the product container is in the shape of a four-sided pyramid. In another embodiment, a fourth sidewall contiguous with at least two of the three sidewalls forming the container is provided, and the connector wall is substantially square in shape and contiguous with each of said at least four sidewalls. In a particular embodiment, the four sidewalls are triangular in shape, whereby the container is in the shape of a five-sided pyramid. A decoration or indicia may also be formed on or in the connector wall to identify the product or enhance the aesthetic appearance of the container, and a cap may be provided for covering or sealing the opening in the container.
In accordance with a sixth aspect of the invention, a method of forming a container having an open end and a closed end using combined injection and blow molding techniques is disclosed. The method comprises injecting a material through a single side gate into an injection mold cavity having an open end portion, a neck portion, and a closed end portion. The side gate is positioned adjacent to the neck portion and at least part of the mold cavity is bounded by a porous material. The method further includes assisting the material in filling the injection mold cavity using a vacuum in fluid communication with the porous material and cooling the material in the mold cavity to form a tubular preform with a closed end having a substantially smooth outer surface. The preform is then blow molded into a container having a predetermined shape and a substantially smooth outer surface along the closed end as a result of forming the preform using the side gate.
In accordance with a seventh aspect of the invention, a system for molding an aesthetically and functionally enhanced container is disclosed. The system comprises an injection mold including a closed-end mold cavity. An injection material is supplied to the cavity through a side gate to form a tubular preform having an open end and a closed end with a substantially smooth outer surface. At least part of the mold cavity is bounded by a porous material, preferably one having a pore size preferably in the range of between about 5-100 microns. A vacuum source is provided in communication with the porous material for assisting in drawing the material into the mold cavity to form the preform. A blow mold apparatus is also provided for forming the container from the preform such that it has a substantially smooth outer surface adjacent to a closed end.